You are not saying which Year and Model you have.

The #12 Fuse on My Year and Model gose to a few items but notably the Power Window Relay.
So if #12 is dead none of you Power Windows will work.

Also on mine the Heater Blower is hooked to the temp switch and it won't operate till the Enging is up to a certain Temperature (that is what the Manual has to say). I am not sure if that is the same in the defrost position.

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84 300D, 82 Volvo 244Gl Diesel